Wow 39mpg...I can believe it ...what do you normally get and does your girlfriend give audi gas saving drivers lessons!!! :-) Sounds like all the right conditions were met during the drive..e.g. no wind and good fuel. Tell your GF she is a hero on this forum!

Yeah, she was driving at a constant 65mph non stop, I think we were driving through Texas on I40 in Sept of 2006, it was raining on and off. That was the only time the car did that high mpg. My daily average is about 22mph mostly city stop-and-go. I've driven my A4 in the canyon(palomar) and did 17mpg, but we weren't trying to conserve gas during that run :)

Wow, even 22 mpg in city is pretty impressive I would say. Mine is 2007 A4 Quattro(19K
miles). I used to get about 20 mpg in the city. Last few months it's been going down
steadily. Now I get about 2-3 mpg less. Nothing much has changed(my driving
pattern, kind of gas I use, etc. and around 34.5 - 35 psi tyre pressure).

Any ideas? Or is it that mpg goes down as miles add?

sometime after 15k my pvc valve went bad...they know about it so tell them to check it due to gas mileage decrease...known bad pvc valves from a supplier.

Are you chipped?

Well, I've noticed my mpg has dropped down this past week. I took my car to the dealer to have it serviced last week and they had a new ecu software upgrade. Service guy told me that my can hasn't been flashed with the new one and it requires it. The flash erased my APR programs, I'm sure that caused the drop in my mpg.

No man, I haven't chipped. Something else is screwed up, no idea.
May be what phospateb suggested, will ask the dealer to take a look during
the next service(comping up in another 3K miles).

And what you plan to do about your problem, take it back to the dealer?

I'm gonna take it to a shop to have the APR programs loaded back on. My car feels soooooooo slow with the stock program.

Like Phosphateb said, the DV and PCV does go bad. Have the dealer run a pressure check, one of them or maybe both could be leaking......mine did and they replaced it with upgraded versions for free.